WHAT IS A THYROD NODULE?
Thyroid nodules are cystic (fluid-filled) or solid (solid, non-liquid) masses in the thyroid gland, which are formed as a result of excessive proliferation of the cells that make up the gland. Although the vast majority of thyroid nodules are benign (non-cancerous), a small proportion involve thyroid cancer. Evaluation of most thyroid nodules is necessary to diagnose and treat thyroid cancer at its earliest stage.
WHY DOES A THYROID NODULE OCCUR?
The cause of a thyroid nodule is generally unknown. Hashimoto’s thyroiditis, the most common cause of hypothyroidism, can cause a thyroid nodule. It is known that iodine deficiency, which is common in our country, causes thyroid nodules. Some nodules may gain autonomy over time and secrete excessive amounts of thyroid hormone, causing hyperthyroidism (hyperfunctioning thyroid nodule as in toxic adenoma, toxic multinodular goiter).
Thyroid nodules are common lesions. A thyroid nodule is detected by examination or imaging in about half of people who reach the age of 60 in the community. More than 90% of these nodules are benign. The majority are found as colloidal nodules, thyroid cysts or follicular neoplasms, less than 10% of the nodules may also be due to thyroid cancer.
WHAT ARE THE SYMPTOMS OF A THYROID NODULE?
Most thyroid nodules have no symptoms. Rarely, they can cause pain, difficulty swallowing, shortness of breath, hoarseness, or symptoms of hyperthyroidism.
HOW IS A THYROID NODULE DETECTED AND EVALUATED?
Thyroid nodules are discovered incidentally during a routine physical examination or during a neck ultrasound or CT scan performed for another reason. Sometimes, patients find thyroid nodules themselves by accidentally noticing a lump on their neck while looking in the mirror.
When a thyroid nodule is detected, it is necessary to determine whether the rest of the thyroid is healthy, whether there are other nodule(s) and whether there is a functional disorder in the thyroid gland, such as hyperthyroidism or hypothyroidism. For this purpose, thyroid function tests should be checked. In addition, thyroid ultrasonography and fine needle biopsy should be performed for more detailed evaluation.
Thyroid ultrasound is an important imaging modality for thyroid nodule evaluation. High-frequency sound waves are used to obtain an image of the thyroid. Thyroid ultrasound can determine whether the nodule is solid or cystic (fluid-filled), as well as determine the exact size and characteristics of the nodule. Thus, it can help identify suspicious nodules for cancer. Thyroid ultrasound can also detect nodules that are too small to be felt during physical examination, thus determining the actual number of nodules. After the initial evaluation is completed, thyroid ultrasound is also useful in the follow-up of nodules to determine size and feature changes.
In addition, ultrasound can be used to do this when a fine needle biopsy is required.
THYROID FINE NEEDLE ASPIRATION BIOPSY (TIIAB)
It is a simple procedure that can be performed without the need for local anesthesia. It usually does not require any special preparation, only if there is use of blood thinners, it may need to be discontinued a few days before the procedure.
A very fine needle is used to draw the cells in the thyroid nodule while performing TIAB, and several samples are taken from different parts of the nodule to increase the chance of getting the most accurate result. The cells are then examined under a microscope by a pathologist.
Thyroid fine-needle aspiration biopsy results may be reported as follows:
The nodule is benign (not cancerous).
About 80% of biopsies are like this. Its false negative rate is less than 3%. Benign thyroid nodules do not require surgery unless they cause symptoms such as shortness of breath or difficulty swallowing. It is enough to follow. It may be necessary to repeat the biopsy if the nodule enlarges or changes over time.
The nodule is malignant (cancer) or suspicious for malignancy (cancer).
About 5% of biopsies are reported as malignant and are mostly caused by papillary cancer, the most common type of thyroid cancer. A suspicious nodule for malignancy carries a 60-75% cancer risk. Nodules with both these diagnoses should be surgically removed.
The structure of the nodule could not be determined (uncertain).
This expression, which can be seen in up to 20% of biopsy results, may indicate several different diagnoses. The definition of “indeterminate” means that although a sufficient number of cells are removed during a fine-needle biopsy, microscopy cannot reliably classify the result as benign or cancerous.
“Follicular lesion” may be one of the diagnoses that cause vague reporting. Approximately 20-30% of nodules reported as follicular lesions are cancerous. Definitive diagnosis can only be made by surgery. In this case, since the nodule is more likely to be non-cancerous (70-80%), usually only one side of the thyroid, where the nodule is located, is removed (lobectomy). If cancer is detected, the remaining thyroid gland should usually be removed as well. If surgery confirms that there is no cancer, no additional surgery is required to “complete” the surgery to remove the remaining thyroid.
Other diagnoses that cause uncertain reporting may be Atypia of Undetermined Significance (AUS) or Follicular Lesion of Undetermined Significance = FLUS. Cells in this nodule are defined as indeterminate because they lack characteristics that would place them in one of the other diagnostic categories. These rarely contain cancer, so they need to be reassessed with FNAB, in which case the other option that may be recommended is surgery to remove half of the thyroid containing the nodule (lobectomy).
The biopsy may be non-diagnostic or insufficient.
When FNAB is performed under ultrasound guidance, it is reported in less than 5% of biopsies. This result indicates that not enough cells are obtained to make a diagnosis, but it is common if the nodule is a cyst. These nodules may need reevaluation with a second fine needle biopsy.
Thyroid scintigraphy has been used very frequently in the past to evaluate thyroid nodules. However, thyroid scintigraphy is no longer accepted as a first-line evaluation method, with the demonstration that the accuracy and sensitivity of thyroid ultrasound and FNAB are very high.
Scintigraphy still has an important role in the evaluation of nodules causing hyperthyroidism. Scintigraphy performed on nodules causing hyperthyroidism may support the need for additional evaluation or biopsy. In many other cases, neck ultrasound and FNAB remain the best and most accurate way to evaluate any type of thyroid nodule.
There are newly developed molecular tests that examine the genes in the DNA of thyroid nodules and continue to be developed in a dynamic process. These tests can be useful in determining whether the nodule is cancerous, especially in cases where the FNAB result is uncertain. These special tests are done on samples taken during the normal biopsy procedure. There are also special blood tests that can help evaluate thyroid nodules. However, there are some difficulties in reaching and having these. Preventive (prophylactic) mastectomy can significantly reduce the risk of developing breast cancer, but it should be noted that this surgery is also a serious choice that can have a significant impact on your future life. Preventive mastectomy is performed on one or both breasts to reduce the risk of developing breast cancer.